The present invention relates to a method for forming a three-dimensional implant.
Conventionally, when a body of bone, for example bones of skull, cheek bone, jaw bone or the like is partially lost, implants made of artificial material are implanted in the deficient part, and fixed thereat (reconstruction of deficient portion of bone).
In the conventional art of reconstruction of the deficient bone, material and shape of the implant is very important.
Regarding the material, ceramics which have excellent biocompatibility are widely used.
Regarding the shape, the implant is conventionally formed as follows.
Firstly, based on CT (Computed Tomography) data of a body of bone having a deficient portion, a model corresponding to the body of bone is formed using wood or the like. Then, in a deficient portion of the model, paper-mache pulp or the like is filled to obtain a shape of an implant (i.e., the shape of body of bone to be located at the deficient portion).
When the shape of the implant is determined in such a manner, however, sufficient reproductivity cannot be obtained. For example, bones of skull are typically reproduced as a continuum of smooth spheres. However, the bones of skull are not usually the continuum of the smooth spheres, and curvatures are different at various points. Therefore, the implant which is formed as the continuum of the smooth spheres has less reproductivity. Regarding the cheek bone or jaw bone, it is more difficult to achieve the high reproductivity.
In another case, the shape of an implant is determined as follows.
Firstly, CT images are obtained with respect to a plurality of cross sections of a body of bone having a deficient portion. Then, plate members (i.e., a plurality of slices) made of wood are formed to have shapes corresponding to the body of bone of the cross sections, respectively.
By stacking the plate members, and making the same adhered together, a model corresponding to the entire body of bone having the deficient portion is formed.
Then, at the deficient portion of the model, paper-mache pulp or the like is filled to obtain a shape of the bone which should exist at the deficient portion. The model formed as above has stepped portions, at its side ends, corresponding to the thickness of the plate members.
Next, using resin material, the model is molded to form a female mold. Then, using the female mold, a male mold made of resin is formed. Then, the steps at the side ends of the male mold are cut out using a cutter or the like so that the male mold has a smooth shape without stepped portions. The thus obtained smooth shape is regarded as the shape of the implant.
When the shape of the implant is determined in such a manner, the following deficiencies are known to arise.
In the above-described method, the model is formed using plate members. Since each plate member is relatively thick, it is difficult to form the model of the body of bone having the deficient portion accurately.
Further, according to the above method, the side end of the male mold is grinded down using a cutter to obtain a smooth surface. However, the actual shape of the body of bone at a surface where the bone is cut is not taken into consideration. Such an implant has less shape compatibility with respect to the body of bone.
If a thinner plate is used, it is possible to improve the shape compatibility of the model. However, there is a limitation in reducing the thickness of each plate member, and it would be difficult to obtain sufficient shape compatibility. Further, if the thinner plate members are used to form the model, it will take a relatively long time for forming a model. Therefore, such a method cannot apply to a condition where the deficient condition cannot remain for a considerable period.